As he prepares to publish his memoirs, BBC News Online examines the timeless appeal of musical legend Bob Dylan.

Bob Dylan's unique fusion of rock, country, folk and blues have had an immeasurable influence on contemporary popular music.

His political lyrical content has influenced everyone from The Beatles to U2, to Bruce Springsteen and Badly Drawn Boy.

Joe Strummer said Dylan "laid down the template" for lyric, tune, seriousness, spirituality and depth of rock music.

And at the age of 63, the man born Robert Alan Zimmerman on 24 May 1941 in Hibbing, Minnesota, is still on the road, still with his own, enduring career.

Globalisation

To his younger fans, for whom records are a quaint reminder of another era, Dylan has as much to say about the environment and globalisation as he had to their parents about racial tolerance and war.

Of the Holy Trinity of Rock, the Beatles self-destructed more than 30 years ago, Elvis turned up his blue suede shoes in 1977, but Dylan continues to surprise and challenge.

Dylan has spent more than 40 years at the top of the music scene

He is currently on tour with Willie Nelson, travelling to Minor League baseball parks across the country US.

In the last few years, two live albums of him performing in 1964 and 1975 have been released.

And in 2002, his album Love and Theft won him a Grammy Award in the contemporary folk album category.

In the fickle and transient world of popular music, Dylan has spent 40 years at the top, constantly re-inventing himself along the way, allowing his fans the opportunity to grow up and grow old with their idol and his music.

For the most part, his songs are easy to play - 100,000 buskers in 100,000 railway stations are testament to that.

He experimented with different sounds

He does not have a conventionally good singing voice. Yet, as a wordsmith, Dylan is unsurpassed. Transcending pop and poetry, his lyrics have provided a soundtrack to his age.

"The answer is blowin' in the wind", "he not busy being born is busy dying" and "there's no success like failure, and failure's no success at all" are almost as much a part of the currency of literature as Shakespeare and Keats.

Earlier this year, Dylan admitted that one of his most famous songs - The Times They Are A-Changin' - was originally a Scottish folk tune.

Songs

Scotland did not seem to mind - he was awarded an honorary degree from St Andrews University in June where he was described as an "iconic figure for the 20th Century".

Even though Dylan has often been dismissive about how much his work reveals about its writer, he admitted in 1990: "People can learn everything about me through my songs, if they know where to look."

To the thousands of amateur Dylanologists, their hero's every concert and out-take is to be recorded, collected and pored over as if it were Holy Writ.

The young Dylan mesmerised a generation

Superfans, like the celebrated Larry Lambchop, about whom Dylan once said "this man has seen me play more times than me", constantly follow him around the world.

He once said that his 1966 album Blonde On Blonde came closest to capturing the "wild mercury sound" inside his head and the image of mercury, an element which is constantly in flux and difficult to contain, is an apt one for Bob Dylan.

His chaotic private life includes a 1965 marriage to a former Playboy bunny girl Sara Lowndes, which produced four children before ending in divorce in 1977.

Beside affairs with numerous other women, he had a second secret wife, his backing singer Carol Dennis, with whom he had a daughter.

Alimony, as well as a continuing burning desire to perform, means that Dylan remains constantly on tour.

Though his glory days at the leading edge of popular culture might be behind him, the timelessness of Bob Dylan's work means that his relevance will never be diminished.